Add missing assertion in DiscreteUniform moment unittest

Author: zoj613

pymc/tests/test_distributions_moments.py

@@ -749,6 +749,7 @@ def test_hyper_geometric_moment(N, k, n, size, expected):
 def test_discrete_uniform_moment(lower, upper, size, expected):
     with Model() as model:
         DiscreteUniform("x", lower=lower, upper=upper, size=size)
+        assert_moment_is_expected(model, expected)
 
 
 @pytest.mark.parametrize(